The present invention relates to an inflatable seatbelt system having a webbing at least a part of which is formed in the shape of a bag and which is maintained in a strap-like configuration under normal circumstances but, when an emergency situation occurs, inflates by the action of a gas supplied from a gas generating device.
Hitherto, seatbelt systems have been attached to the seats of many vehicles, for example, automobiles. A typical seatbelt system is arranged to restrain the occupant's body by a webbing upon the occurrence of an emergency situation, e.g., a collision of the vehicle, thereby protecting the occupant from injury which would otherwise be done to him or her by collision with a part of the vehicle body. In such a seatbelt system, however, the width of the webbing, which constitutes a belt for restraining the occupant's body, is not so large. Therefore, the occupant's body locally receives a relatively heavy load when restrained by the webbing.
Under these circumstances, a variety of inflatable seatbelt systems have been proposed in which the webbing is formed in the shape of a bag, and under normal circumstances, the bag-shaped webbing is maintained in a strap-like configuration so as to function as an ordinary seatbelt, whereas, when an emergency occurs, the bag-shaped webbing is inflated by a gas introduced thereinto from a gas generating device so as to function as an air belt whereby the occupant's body is received by the inflated webbing. For example, see Japanese Patent Application Laid-Open (KOKAI) Nos. 47-26830 and 49-88220. Such an inflatable seatbelt system allows the kinetic energy of the occupant's body to be received by the webbing having a wider area. Thus, the load is dispersed, and hence the occupant's body receives a relatively light load. Accordingly, the occupant is protected even more effectively.
When inflating, the webbing shortens longitudinally and, at the same time, increases in thickness. Consequently, the webbing presses the occupant's body against the seat by an amount corresponding to the increase in the thickness. That is, since the length of the webbing shortens and the thickness thereof increases due to the inflation of the webbing, it is possible to obtain a webbing pull-in effect similar to the effectiveness obtained when the webbing is actually pulled in. Accordingly, the inflatable seatbelt system makes it possible to obtain initial restraining force similar to that provided by a pretensioner.
With the initial restraining force, the inflatable seatbelt system completely restrains the occupant's body during a crashable zone, i.e., a period between the time when a vehicle comes into collision and the time when the front part of the vehicle, gradually crashing, reaches the occupant's body. Accordingly, it is possible to make good use of the crashable zone.
If it is intended to provide a rear seat with an air bag system as is provided for the occupant seated in the front seat, the air bag system must inevitably be provided on the front seat, which lies forwardly of the rear seat. However, if the air bag system is provided on the front seat, it is difficult for the air bag system to protect the rear seat occupant properly and effectively because the position in the longitudinal direction of the front seat depends on the occupant seated therein and the reclining position also differs according to circumstances. Accordingly, the above-described inflatable seatbelt system is particularly effective as a safety device for the rear seat.
Incidentally, to introduce a gas generated by a gas generating device into a bag-shaped portion of a webbing, one method can be conceived in which the bag-shaped portion of the webbing is connected to a tongue formed with a gas flow hole in such a manner that the gas flow hole opens in the bag-shaped portion, and a buckle device is provided with the gas generating device and formed with a gas flow hole for the gas generated from the gas generating device so that when the tongue is engaged with the buckle device, the respective gas flow holes of the tongue and the buckle device are communicated with each other, thereby enabling the gas from the gas generating device to be introduced into the bag-shaped portion of the webbing through the two gas flow holes.
The above-described gas introducing method involves the problem of how to connect the bag-shaped portion of the webbing to the tongue. Methods which have heretofore been conceived include those which are shown in FIG. 8. According to one conventional method, as shown in FIG. 8(a), the opening end of the bag-shaped portion of the webbing 11 is inserted into the gas flow hole 5g of the tongue 5, and a lock member 17 is inserted into the opening of the bag-shaped portion and then expanded to clamp the opening end of the bag-shaped portion between the inner peripheral surface of the gas flow hole 5g of the tongue 5 and the outer peripheral surface of the lock member 17.
According to another conventional method, as shown in FIG. 8(b), the end of the tongue 5 where the gas flow hole 5g opens is inserted into the opening end of the bag-shaped portion of the webbing 11, and a lock member 17 is fitted onto the outer periphery of the opening end of the bag-shaped portion and then contracted from the outer side thereof, thereby clamping the opening end of the bag-shaped portion between the outer peripheral surface of the opening end of the tongue 5, where the gas flow hole 5g opens, and the inner peripheral surface of the lock member 17, in a manner reverse to the method shown in FIG. 8(a).
Still another conventional method is similar to the method shown in FIG. 8(b). In this method, however, the opening end of the tongue 5, where the gas flow hole 5g opens, is enlarged in diameter to form an enlarged-diameter portion 5j, as shown in FIG. 8(c), and the opening end of the bag-shaped portion is clamped between the enlarged-diameter portion 5j and the lock member 17.
Incidentally, in the inflatable seatbelt system, when deceleration rapidly acts on the vehicle, large tension is longitudinally applied to the webbing not only by the inertia acting on the occupant's body but also by the expansion force resulting from the inflation of the bag-shaped portion of the webbing caused by the gas from the gas generating device.
With the above-described conventional methods of connecting together the bag-shaped portion of the webbing and the tongue, however, the strength of the connection between these two members with respect to the tension acting in the longitudinal direction of the webbing is not very high because in the conventional methods the webbing is merely clamped in the radial direction, and it is necessary to increase the strength of the connection to a sufficiently high level in order to enable the large longitudinal tension to be surely received.
If it is intended to increase the strength of the connection made by the above-described conventional methods, the joint of the tongue and the bag-shaped portion of the webbing becomes relatively large in size. However, if the joint increases in size, the operatability of the tongue deteriorates. In addition, it is difficult for the seatbelt to fit smoothly to the occupant's body when it is fastened thereto.